The long-term objective of the proposed research is to determine mechanisms linking intermediary metabolism to reproductive activity. This will lead to improved understanding of the causes of infertility associated with malnutrition, anorexia nervosa and intense athletic training. The specific aims of this research are to (1) test the hypothesis that the low level of luteinizing hormone (LH) release caused by undernutrition in ewe lambs is associated with decreased insulin release and altered brain uptake of tyrosine and tryptophan, precursors for neurotransmitters which influence LH release, (2) test the hypothesis that insulin mediates the effects of nutrition on LH release by acting directly on the central nervous system, and (3) test the hypothesis that tyrosine and tryptophan influence patterns of LH release. Prepubertal ewe lambs subjected to restricted or ad libitum feeding will be utilized in these experiments. In the first experiment, brain uptake of tyrosine and tryptophan will be estimated by collecting simultaneous blood samples from the cerebral vein and carotid artery and determining arteriovenous differences in concentrations of these amino acids. The second experiment will examine the effect of intraventricular infusion of insulin on LH release in underfed lambs. The third and fourth experiments will focus on the effects of tyrosine and tryptophan on LH release in lambs. Circulating concentrations of these amino acids will be elevated via continuous infusion into the abomasum.